001 /* 002 $Id: RootLoader.java 3870 2006-06-28 12:59:18Z blackdrag $ 003 004 Copyright 2003 (C) Jochen Theodorou. All Rights Reserved. 005 006 Redistribution and use of this software and associated documentation 007 ("Software"), with or without modification, are permitted provided 008 that the following conditions are met: 009 010 1. Redistributions of source code must retain copyright 011 statements and notices. Redistributions must also contain a 012 copy of this document. 013 014 2. Redistributions in binary form must reproduce the 015 above copyright notice, this list of conditions and the 016 following disclaimer in the documentation and/or other 017 materials provided with the distribution. 018 019 3. The name "groovy" must not be used to endorse or promote 020 products derived from this Software without prior written 021 permission of The Codehaus. For written permission, 022 please contact info@codehaus.org. 023 024 4. Products derived from this Software may not be called "groovy" 025 nor may "groovy" appear in their names without prior written 026 permission of The Codehaus. "groovy" is a registered 027 trademark of The Codehaus. 028 029 5. Due credit should be given to The Codehaus - 030 http://groovy.codehaus.org/ 031 032 THIS SOFTWARE IS PROVIDED BY THE CODEHAUS AND CONTRIBUTORS 033 ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT 034 NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND 035 FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL 036 THE CODEHAUS OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 037 INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 038 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 039 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 040 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 041 STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 042 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 043 OF THE POSSIBILITY OF SUCH DAMAGE. 044 045 */ 046 package org.codehaus.groovy.tools; 047 048 import java.net.URL; 049 import java.net.URLClassLoader; 050 051 /** 052 * This ClassLoader should be used as root of class loaders. Any 053 * RootLoader does have it's own classpath. When searching for a 054 * class or resource this classpath will be used. Parent 055 * Classloaders are ignored first. If a class or resource 056 * can't be found in the classpath of the RootLoader, then parent is 057 * checked. 058 * 059 * <b>Note:</b> this is very against the normal behavior of 060 * classloaders. Normal is to frist check parent and then look in 061 * the ressources you gave this classloader. 062 * 063 * It's possible to add urls to the classpath at runtime through 064 * @see #addURL(URL) 065 * 066 * <b>Why using RootLoader?</b> 067 * If you have to load classes with multiple classloaders and a 068 * classloader does know a class which depends on a class only 069 * a child of this loader does know, then you won't be able to 070 * load the class. To load the class the child is not allowed 071 * to redirect it's search for the class to the parent first. 072 * That way the child can load the class. If the child does not 073 * have all classes to do this, this fails of course. 074 * 075 * For example: 076 * 077 * <pre> 078 * parentLoader (has classpath: a.jar;c.jar) 079 * | 080 * | 081 * childLoader (has classpath: a.jar;b.jar;c.jar) 082 * </pre> 083 * 084 * class C (from c.jar) extends B (from b.jar) 085 * 086 * childLoader.find("C") 087 * --> parentLoader does know C.class, try to load it 088 * --> to load C.class it has to load B.class 089 * --> parentLoader is unable to find B.class in a.jar or c.jar 090 * --> NoClassDefFoundException! 091 * 092 * if childLoader had tried to load the class by itself, there 093 * would be no problem. Changing childLoader to be a RootLoader 094 * instance will solve that problem. 095 * 096 * @author Jochen Theodorou 097 */ 098 public class RootLoader extends URLClassLoader { 099 100 /** 101 * constructs a new RootLoader without classpath 102 * @param parent the parent Loader 103 */ 104 private RootLoader(ClassLoader parent) { 105 this(new URL[0],parent); 106 } 107 108 /** 109 * constructs a new RootLoader with a parent loader and an 110 * array of URLs as classpath 111 */ 112 public RootLoader(URL[] urls, ClassLoader parent) { 113 super(urls,parent); 114 } 115 116 private static ClassLoader chooseParent(){ 117 ClassLoader cl = RootLoader.class.getClassLoader(); 118 if (cl!=null) return cl; 119 return ClassLoader.getSystemClassLoader(); 120 } 121 122 /** 123 * constructs a new RootLoader with a @see LoaderConfiguration 124 * object which holds the classpath 125 */ 126 public RootLoader(LoaderConfiguration lc) { 127 this(chooseParent()); 128 Thread.currentThread().setContextClassLoader(this); 129 URL[] urls = lc.getClassPathUrls(); 130 for (int i=0; i<urls.length; i++) { 131 addURL(urls[i]); 132 } 133 } 134 135 /** 136 * loads a class using the name of the class 137 */ 138 protected Class loadClass(final String name, boolean resolve) throws ClassNotFoundException { 139 Class c = this.findLoadedClass(name); 140 if (c!=null) return c; 141 142 try { 143 c = findClass(name); 144 } catch (ClassNotFoundException cnfe) {} 145 if (c==null) c= super.loadClass(name,resolve); 146 147 if (resolve) resolveClass(c); 148 149 return c; 150 } 151 152 /** 153 * returns the URL of a resource, or null if it is not found 154 */ 155 public URL getResource(String name) { 156 URL url = findResource(name); 157 if (url==null) url=super.getResource(name); 158 return url; 159 } 160 161 /** 162 * adds an url to the classpath of this classloader 163 */ 164 public void addURL(URL url) { 165 super.addURL(url); 166 } 167 }